Image encoding and decoding method supporting plurality of layers and apparatus using same

ABSTRACT

An image decoding method supporting a plurality of layers according to the present invention may comprise the steps of: receiving location information on a location in which an inter-layer reference picture set for one or more reference layers, to which a current picture can refer, is added to a reference picture list; generating an initial reference picture list including the inter-layer reference picture set on the basis of the location information; and predicting the current picture on the basis of the initial reference picture list. Accordingly, the present invention provides a method for signaling location information on a location in which an inter-layer reference picture is added to a reference picture list, and an apparatus using the same.

CROSS REFERENCE TO RELATED APPLICATIONS

The application is a Continuation of U.S. patent application Ser. No.14/908,230 (filed on Jan. 28, 2016), which is a National Stage PatentApplication of PCT International Patent Application No.PCT/KR2014/006793 (filed on Jul. 25, 2014) under 35 U.S.C. § 371, whichclaims priority to Korean Patent Application Nos. 10-2013-0090227 (filedon Jul. 30, 2013) and 10-2013-0125928 (filed on Oct. 22, 2013), theteachings of which are incorporated herein in their entireties byreference.

TECHNICAL FIELD

The present invention generally relates to video compression technologyand, more particularly, to a method and device for performing videocoding that supports a multi-layer structure.

BACKGROUND ART

Recently, demand for high-resolution, high-quality video such as HD(High Definition) video and UHD (Ultra High Definition) video isincreasing in various application fields. As video data hashigh-resolution, high-quality images, the amount of data is higher thanfor existing video data. Therefore, when the video data is transmittedusing media such as existing wired and wireless broadband lines or isstored in existing storage media, transmission costs and storage costsincrease. To solve these problems caused by the high-resolution andhigh-quality video data, high-efficiency video compression techniquesmay be used.

As video compression techniques, there are various techniques such as aninter-prediction technique for predicting the values of pixels includedin a current picture from pictures that precede or follow the currentpicture, an intra-prediction technique for predicting the values ofpixels in the current picture using information about the pixelsincluded in the current picture, an entropy coding technique, in whichthe shortest code is assigned to the most frequently used value and thelongest code is assigned to the least frequently used value, and thelike. Video data may be effectively compressed using these videocompression techniques, and may then be transmitted or stored.

DISCLOSURE Technical Problem

An object of an embodiment of the present invention is to provide amethod for generating, for a target layer to be currently encoded anddecoded, a reference picture list including pictures of another layer,and a device using the method.

Another object of the embodiment of the present invention is to providea method for adaptively including pictures of another layer in areference picture list depending on the characteristics of picture sets,and a device using the method.

An object of another embodiment of the present invention is to provide amethod for partitioning reference pictures of another layer andincluding the partitioned reference pictures in a reference picturelist, and a device using the method.

Another object of the other embodiment of the present invention is toprovide a method for adaptively including reference pictures of anotherlayer in a reference picture list depending on the sequence of views,and a device using the method.

A further object of the other embodiment of the present invention is toprovide a method for adaptively including pictures of another layer in areference picture list depending on the index value of the temporalsub-layer of a current picture, and a device using the method.

An object of a further embodiment of the present invention is to providea method for adaptively including pictures of another layer in areference picture list depending on the difference between the indexvalues of temporal sub-layers of layers, and a device using the method.

An object of yet another embodiment of the present invention is toprovide a method for signaling position information about the positionto which an inter-layer reference picture is added in a referencepicture list, and a device using the method.

Technical Solution

A video decoding method for decoding a video supporting multiple layersaccording to an embodiment of the present invention includes receivinginformation about a position, to which an inter-layer reference pictureset for at least one reference layer that is capable of being referredto by a current picture is to be added, in a reference picture list;generating an initial reference picture list including the inter-layerreference picture set based on the position information; and performingprediction of the current picture based on the initial reference picturelist.

The video decoding method may further include generating a short-termreference picture set and a long-term reference picture set, eachincluding pictures present in a layer identical to that of the currentpicture, wherein generating the initial reference picture list isconfigured to add, based on the position information, the inter-layerreference picture set to a position in the initial reference picturelist, indicated by the position information.

The position information may be received, with the position informationbeing included in a slice header or a sequence header.

Receiving the position information may include receiving an indicationflag that indicates whether an indication index indicating the position,to which an inter-layer reference picture that is capable of beingreferred to by the current picture is to be added, in the initialreference picture list has been transmitted; and receiving theindication index when the indication flag is 1.

The indication flag may be received, with the indication flag beingincluded in a video parameter set of each layer.

The indication index may be received, with the indication index beingincluded in a slice header or a sequence header.

The initial reference picture list may include initial reference picturelist 0, and the initial reference picture list 0 may be constructed in asequence of a short-term reference picture set including short-termreference pictures having Picture Order Counts (POCs) less than that ofthe current picture, the inter-layer reference picture set, a short-termreference picture set including short-term reference pictures havingPOCs greater than that of the current picture, and a long-term referencepicture set including long-term reference pictures.

The initial reference picture list may include initial reference picturelist 1, and the initial reference picture list 1 may be constructed in asequence of a short-term reference picture set including short-termreference pictures having POCs greater than that of the current picture,the inter-layer reference picture set, a short-term reference pictureset including short-term reference pictures having POCs less than thatof the current picture, and a long-term reference picture set includinglong-term reference pictures.

The inter-layer reference picture set may include a first sub-referencelayer picture set and a second sub-reference layer picture set, and thefirst sub-reference layer picture set and the second sub-reference layerpicture set are separated and aligned in the initial reference picturelist.

The inter-layer reference picture set may include multiview referencelayer pictures, the initial reference picture list may include initialreference picture list 0, and the initial reference picture list 0 isaligned in a sequence of a short-term reference picture set includingshort-term reference pictures having POCs less than that of the currentpicture, the first sub-reference layer picture set including pictureshaving a view sequential position lower than that of the current pictureamong the multiview reference layer pictures, a short-term referencepicture set including short-term reference pictures having POCs greaterthan that of the current picture, a long-term reference picture setincluding long-term reference pictures, and the second sub-referencelayer picture set including pictures having a view sequential positionhigher than that of the current picture among the multiview referencelayer pictures.

The inter-layer reference picture set may include multiview referencelayer pictures, the initial reference picture list comprises initialreference picture list 1, and the initial reference picture list 1 isaligned in a sequence of a short-term reference picture set includingshort-term reference pictures having POCs greater than that of thecurrent picture, the second sub-reference layer picture set includingpictures having a view sequential position higher than that of thecurrent picture among the multiview reference layer pictures, ashort-term reference picture set including short-term reference pictureshaving POCs less than that of the current picture, a long-term referencepicture set including long-term reference pictures, and the firstsub-reference layer picture set including pictures having a viewsequential position lower than that of the current picture among themultiview reference layer pictures.

The video decoding method may further include receiving flag informationthat indicates whether the inter-layer reference picture set isseparated into at least two sub-reference layer picture sets and thenadded to the reference picture list.

The video decoding method may further include, when the flag informationis 1, receiving information about a number of sub-reference layerpicture sets into which the inter-layer reference picture set isseparated.

Generating the inter-layer reference picture set may be performed basedon a temporal sub-layer index (tempralId) of the current picture.

Generating the inter-layer reference picture set may be performed basedon a maximum number of temporal sub-layers to which inter-layerprediction is permitted.

The video decoding method may further include generating a finalreference picture list by modifying the initial reference picture list.

Performing prediction of the current picture may be configured to usereference pictures included in the inter-layer reference picture set asreference pictures of the current picture.

A video decoding device for decoding video supporting multiple layersaccording to another embodiment of the present invention includes anentropy decoding part for decoding information required for predictionand decoding of video received via a bitstream; and a prediction partfor deriving information about a position, to which an inter-layerreference picture set for at least one reference layer that is capableof being referred to by a current picture is to be added, in a referencepicture list, generating an initial reference picture list including theinter-layer reference picture set based on the position information, andperforming prediction of the current picture based on the initialreference picture list.

Advantageous Effects

In accordance with an embodiment of the present invention, there areprovided a method for generating, for a target layer to be currentlyencoded and decoded, a reference picture list including pictures ofanother layer, and a device using the method.

Further, in accordance with the embodiment of the present invention,there are provided a method for adaptively including pictures of anotherlayer in a reference picture list depending on the characteristics ofpicture sets, and a device using the method.

Meanwhile, in accordance with another embodiment of the presentinvention, there are provided a method for partitioning referencepictures of another layer and including the partitioned referencepictures in a reference picture list, and a device using the method.

In accordance with the other embodiment of the present invention, thereare provided a method for adaptively including reference pictures ofanother layer in a reference picture list depending on the sequence ofviews, and a device using the method.

Furthermore, in accordance with the other embodiment of the presentinvention, there are provided a method for adaptively including picturesof another layer in a reference picture list depending on the indexvalue of the temporal sub-layer of a current picture, and a device usingthe method.

In accordance with a further embodiment of the present invention, thereare provided a method for adaptively including pictures of another layerin a reference picture list depending on the difference between theindex values of temporal sub-layers of layers, and a device using themethod.

In accordance with yet another embodiment of the present invention is toprovide a method for signaling position information about the positionto which an inter-layer reference picture is added in a referencepicture list, and a device using the method.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram schematically showing an encoding deviceaccording to an embodiment of the present invention;

FIG. 2 is a block diagram schematically showing a decoding deviceaccording to an embodiment of the present invention;

FIG. 3 is a conceptual diagram showing an example of a reference pictureset that includes short-term reference pictures;

FIG. 4 is a conceptual diagram illustrating a method for deriving thePicture Order Count (POC) of long-term reference pictures;

FIG. 5 is a diagram showing an example in which a reference picture listis constructed;

FIG. 6 is a conceptual diagram showing an example in which aninter-layer reference picture list is constructed according to anembodiment of the present invention;

FIG. 7 is a diagram showing the construction of reference picture list 0according to an embodiment of the present invention;

FIG. 8 is a diagram showing the construction of reference picture list 0according to another embodiment of the present invention;

FIG. 9 is a diagram showing the construction of reference picture list 1according to an embodiment of the present invention;

FIG. 10 is a diagram showing the construction of reference picture list1 according to another embodiment of the present invention;

FIG. 11 illustrates a reference picture list constructed using temporalsub-layer indices according to an embodiment of the present invention;

FIG. 12 illustrates a reference picture list constructed using multiviewreference pictures according to an embodiment of the present invention;

FIG. 13 is a diagram illustrating a method for generating a referencepicture list according to an embodiment of the present invention; and

FIG. 14 is a diagram showing a method for generating a reference picturelist according to another embodiment of the present invention.

BEST MODE

A video decoding method for decoding a video supporting multiple layersaccording to an embodiment of the present invention includes receivinginformation about a position, to which an inter-layer reference pictureset for at least one reference layer that is capable of being referredto by a current picture is to be added, in a reference picture list;generating an initial reference picture list including the inter-layerreference picture set based on the position information; and performingprediction of the current picture based on the initial reference picturelist.

The video decoding method may further include generating a short-termreference picture set and a long-term reference picture set, eachincluding pictures present in a layer identical to that of the currentpicture, wherein generating the initial reference picture list isconfigured to add, based on the position information, the inter-layerreference picture set to a position in the initial reference picturelist, indicated by the position information.

The position information may be received, with the position informationbeing included in a slice header or a sequence header.

Receiving the position information may include receiving an indicationflag that indicates whether an indication index indicating the position,to which an inter-layer reference picture that is capable of beingreferred to by the current picture is to be added, in the initialreference picture list has been transmitted; and receiving theindication index when the indication flag is 1.

The indication flag may be received, with the indication flag beingincluded in a video parameter set of each layer.

The indication index may be received, with the indication index beingincluded in a slice header or a sequence header.

The initial reference picture list may include initial reference picturelist 0, and the initial reference picture list 0 may be constructed in asequence of a short-term reference picture set including short-termreference pictures having Picture Order Counts (POCs) less than that ofthe current picture, the inter-layer reference picture set, a short-termreference picture set including short-term reference pictures havingPOCs greater than that of the current picture, and a long-term referencepicture set including long-term reference pictures.

The initial reference picture list may include initial reference picturelist 1, and the initial reference picture list 1 may be constructed in asequence of a short-term reference picture set including short-termreference pictures having POCs greater than that of the current picture,the inter-layer reference picture set, a short-term reference pictureset including short-term reference pictures having POCs less than thatof the current picture, and a long-term reference picture set includinglong-term reference pictures.

The inter-layer reference picture set may include a first sub-referencelayer picture set and a second sub-reference layer picture set, and thefirst sub-reference layer picture set and the second sub-reference layerpicture set are separated and aligned in the initial reference picturelist.

The inter-layer reference picture set may include multiview referencelayer pictures, the initial reference picture list may include initialreference picture list 0, and the initial reference picture list 0 isaligned in a sequence of a short-term reference picture set includingshort-term reference pictures having POCs less than that of the currentpicture, the first sub-reference layer picture set including pictureshaving a view sequential position lower than that of the current pictureamong the multiview reference layer pictures, a short-term referencepicture set including short-term reference pictures having POCs greaterthan that of the current picture, a long-term reference picture setincluding long-term reference pictures, and the second sub-referencelayer picture set including pictures having a view sequential positionhigher than that of the current picture among the multiview referencelayer pictures.

The inter-layer reference picture set may include multiview referencelayer pictures, the initial reference picture list comprises initialreference picture list 1, and the initial reference picture list 1 isaligned in a sequence of a short-term reference picture set includingshort-term reference pictures having POCs greater than that of thecurrent picture, the second sub-reference layer picture set includingpictures having a view sequential position higher than that of thecurrent picture among the multiview reference layer pictures, ashort-term reference picture set including short-term reference pictureshaving POCs less than that of the current picture, a long-term referencepicture set including long-term reference pictures, and the firstsub-reference layer picture set including pictures having a viewsequential position lower than that of the current picture among themultiview reference layer pictures.

The video decoding method may further include receiving flag informationthat indicates whether the inter-layer reference picture set isseparated into at least two sub-reference layer picture sets and thenadded to the reference picture list.

The video decoding method may further include, when the flag informationis 1, receiving information about a number of sub-reference layerpicture sets into which the inter-layer reference picture set isseparated.

Generating the inter-layer reference picture set may be performed basedon a temporal sub-layer index (tempralId) of the current picture.

Generating the inter-layer reference picture set may be performed basedon a maximum number of temporal sub-layers to which inter-layerprediction is permitted.

The video decoding method may further include generating a finalreference picture list by modifying the initial reference picture list.

Performing prediction of the current picture may be configured to usereference pictures included in the inter-layer reference picture set asreference pictures of the current picture.

A video decoding device for decoding video supporting multiple layersaccording to another embodiment of the present invention includes anentropy decoding part for decoding information required for predictionand decoding of video received via a bitstream; and a prediction partfor deriving information about a position, to which an inter-layerreference picture set for at least one reference layer that is capableof being referred to by a current picture is to be added, in a referencepicture list, generating an initial reference picture list including theinter-layer reference picture set based on the position information, andperforming prediction of the current picture based on the initialreference picture list.

MODE FOR INVENTION

Element modules described in the embodiments and drawings of the presentinvention are independently shown in order to indicate different andcharacteristic functions of a video encoding device. However, this doesnot mean that each of the element modules is formed of a separate pieceof hardware or software. That is, the element modules are arranged andincluded for convenience of description, and at least two of the elementmodules may form one element module or one element module may be dividedinto a plurality of element modules to perform their own functions. Anembodiment in which the element modules are integrated and an embodimentin which the element modules are separated are included in the scope ofthe present invention, unless it departs from the essence of the presentinvention.

Further, some elements disclosed in the present invention are notessential elements for performing essential functions, but may beoptional elements for improving only performance. The present inventionmay be implemented using only essential elements for implementing theessence of the present invention, without elements used merely toimprove performance, and a structure including only essential elements,but not optional elements used only to improve performance, is includedin the scope of the present invention.

The present invention may be variously changed and may have variousembodiments, and specific embodiments will be described in detail belowwith reference to the attached drawings. However, it should beunderstood that those embodiments are not intended to limit the presentinvention to specific disclosure forms and they include all changes,equivalents or modifications included in the spirit and scope of thepresent invention. The terms used in the present specification aremerely used to describe specific embodiments and are not intended tolimit the present invention. A singular expression includes a pluralexpression unless a description to the contrary is specifically pointedout in context. In the present specification, it should be understoodthat the terms such as “include” or “have” are merely intended toindicate that features, numbers, steps, operations, components, parts,or combinations thereof are present, and are not intended to exclude thepossibility that one or more other features, numbers, steps, operations,components, parts, or combinations thereof will be present or added.

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. In the followingdescription of the present invention, the same reference numerals areused to designate the same or similar components throughout the drawingsand repeated descriptions of the same components will be omitted.

Video encoding and decoding that support multiple layers in a bitstreamare referred to as “scalable coding”. Since there is a strongcorrelation between multiple layers, duplicate elements in data may beremoved and the encoding performance of video may be improved ifprediction is performed based on such correlation. Hereinafter,predicting the current layer, which is the target of prediction, usinginformation about another layer is referred to as “inter-layerprediction”.

At least one of a resolution, a frame rate, and a color format may bedifferent between the multiple layers, and up-sampling or down-samplingmay be performed in order to adjust the resolution during theinter-layer prediction.

FIG. 1 is a block diagram schematically illustrating an encoding deviceaccording to an embodiment of the present invention.

An encoding device 100 according to the present invention includes anencoding unit 100 a for an upper layer and an encoding unit 100 b for alower layer.

The upper layer may be called a current layer or an enhancement layer,and the lower layer may be called a reference layer or a base layer. Atleast one of the resolution, frame rate, and color format may differbetween the upper layer and the lower layer. When a change of resolutionis required for inter-layer prediction, up-sampling or down-sampling ofthe layer may be performed.

The encoding unit 100 a for the upper layer may include a partitioningunit 110, a prediction unit 100, an intra-prediction unit 121, aninter-prediction unit 122, an inter-layer prediction unit 123, atransform unit 130, a quantization unit 140, a rearrangement unit 150,an entropy coding unit 160, an inverse quantization unit 170, aninverse-transform unit 180, a filter unit 190, a memory 195, and amultiplexer (MUX) 197.

The encoding unit 100 b for the lower layer may include a partitioningunit 111, a prediction unit 125, an intra-prediction unit 126, aninter-prediction unit 127, a transform unit 131, a quantization unit141, a rearrangement unit 151, an entropy coding unit 161, an inversequantization unit 171, an inverse-transform unit 181, a filter unit 191,and a memory 196.

The encoding unit may be implemented by a video encoding methoddescribed in an embodiment of the present invention, which will bedescribed below, but the operations of some units may not be performedin order to reduce the complexity of the encoding device or to enablefast real-time encoding. For example, rather than a method in which allintra-prediction mode methods are used to select the optimalintra-encoding method, a method in which one is selected from among alimited number of intra-prediction modes and the selected one is set asthe final intra-prediction mode may be performed for real-time encodingwhen the prediction unit performs intra-prediction. In another example,a shape of a prediction block used for intra-prediction orinter-prediction may have a limited form.

The unit of a block processed in the encoding device may be a codingunit for performing coding, a prediction unit for performing prediction,or a transform unit for performing transformation. The coding unit, theprediction unit, and the transform unit may be represented as CU, PU,and TU, respectively.

Each of the partitioning units 110 and 111 may partition a layer pictureinto multiple combinations of coding blocks, prediction blocks, andtransform blocks, and may partition a layer by selecting one combinationof coding blocks, prediction blocks, and transform blocks based on apredetermined reference (for example, a cost function). For example, inorder to partition a layer picture into coding units, a recursive treestructure such as a QuadTree structure may be used. Hereinafter, in anembodiment of the present invention, a coding block may mean not only ablock for encoding but also a block for decoding.

A prediction block may be a unit for performing prediction, such asintra-prediction or inter-prediction. A block for intra-prediction maybe a block having the form of a square, such as 2N×2N or N×N. As a blockfor inter-prediction, there are a block in the form of a square, such as2N×2N and N×N, a block in the form of 2N×N and N×2N, obtained bybisecting a prediction block having a square form, and a block having anasymmetric form, obtained by a prediction block partitioning methodusing Asymmetric Motion Partitioning (AMP). The transform unit 115 mayuse different transform methods depending on the form of the predictionblock.

Each of the prediction units 120 and 125 of the encoding units 100 a and100 b may include an intra-prediction unit 121 or 126 for performingintra-prediction and an inter-prediction unit 1122 or 126 for performinginter-prediction. The prediction unit 120 of the encoding unit 100 a forthe upper layer further includes an inter-layer prediction unit 123,which performs prediction of the upper layer using the information aboutthe lower layer.

Each of the prediction units 120 and 125 may determine whether toperform inter-prediction or intra-prediction of a prediction block. Theprocessing unit on which prediction is performed may be different fromthe unit of the processing block for determining the prediction method.For example, when intra-prediction is performed, the prediction mode maybe determined based on a prediction block, and the prediction processmay be performed based on a transform block. A residual (residual block)between the generated prediction block and the original block may beinput to the transform units 130 and 131. Also, the prediction modeinformation used for prediction, motion vector information, and the likeare encoded along with the residual by the entropy coding unit 130, andthen may be transmitted to the decoding device.

When a Pulse Code Modulation (PCM) encode mode is used, the originalblock may be encoded without performing prediction by the predictionunits 120 and 125, and then may be transmitted to a decoding part.

Each of the intra-prediction units 121 and 126 may generate anintra-predicted block based on reference pixels adjacent to the currentblock (the prediction target block). In the intra-prediction method, theintra-prediction mode may have a directional prediction mode, which usesreference pixel information according to the prediction direction, and anon-directional mode, which does not use direction information whenmaking the prediction. The mode for predicting luma information may bedifferent from the mode for predicting chroma information.Intra-prediction mode information, obtained by predicting lumainformation, or information about the predicted luma signal may be usedto predict chroma information. Meanwhile, if the reference pixels arenot available, a prediction block may be generated by replacing theunavailable reference pixels with other pixels.

A prediction block may include multiple transform blocks. If the size ofa prediction block is the same as the size of a transform block whenperforming intra-prediction, intra-prediction of the prediction blockmay be performed based on a left pixel, an upper-left pixel, and anupper pixel of the prediction block. However, if the prediction blockincludes multiple transform blocks because the size of a predictionblock is different from that of a transform block when performingintra-prediction, intra-prediction may be performed based on referencepixels determined based on the transform block.

The intra-prediction method may generate a prediction block afterapplying a Mode-Dependent Intra Smoothing (MDIS) filter to referencepixels according to the intra-prediction mode. The type of MDIS filterapplied to the reference pixels may vary. The MDIS filter, which is anadditional filter applied to an intra-predicted block generated byperforming intra-prediction, may be used for reducing a residual betweenreference pixels and the intra-predicted block, generated afterperforming prediction. When MDIS filtering is performed, differentfiltering may be performed on reference pixels and on some columnsincluded in the intra-predicted block according to the direction of theintra-prediction mode.

Each of the inter-prediction units 122 and 127 may perform prediction byreferring to the information about a block included in at least one ofthe picture preceding or the picture following the current picture. Eachof the inter-prediction units 122 and 127 may include a referencepicture interpolation unit, a motion prediction unit, and a motioncompensation unit.

The reference picture interpolation unit may receive reference pictureinformation from a memory 195 or 196 and may generate information abouta pixel, which is smaller than an integer pixel, from the referencepicture. For a luma pixel, a DCT-based 8-tap interpolation filter, whichdifferently sets filter coefficients to generate information about apixel that is smaller than an integer pixel in units of ¼ pixels, may beused. For chroma signals, a DCT-based 4-tap interpolation filter, whichdifferently sets filter coefficients to generate information about apixel that is smaller than an integer pixel in units of ⅛ pixels, may beused.

Each of the inter-prediction units 122 and 127 may perform motionprediction based on the reference picture interpolated by the referencepicture interpolation unit. As a method for calculating a motion vector,various methods, such as a Full search-based Block Matching Algorithm(FBMA), a Three-Step Search (TSS) algorithm, and a New Three-Step Search(NTS) Algorithm, may be used. The motion vector may have a motion vectorvalue corresponding to ½ or ¼ of the interpolated pixel. Each of theinter-prediction units 122 and 127 may perform prediction on a currentblock using any one of various inter-prediction methods.

As the inter-prediction method, any of various methods such as a skipmethod, a merge method, and a Motion Vector Prediction (MVP) method maybe used.

In inter-prediction, motion information, that is, information about theindex of a reference picture, a motion vector, and a residual signal, isentropy-coded and then transferred to the decoding unit. When a skipmode is applied, a residual may not be generated, transformed, quantizedor transmitted.

The inter-layer prediction unit 123 performs inter-layer prediction forpredicting an upper layer using information about the lower layer. Theinter-layer prediction unit 123 may perform inter-layer textureprediction, inter-layer motion prediction (inter-layerinter-prediction), inter-layer syntax prediction, etc. using the textureinformation, intra-prediction mode information, motion information,syntax information, etc. of the lower layer.

Inter-layer texture prediction means that the texture of a referenceblock in the lower layer is used as the predicted value (predictionsample) of the current block in the upper layer, wherein the texture ofthe reference block may be scaled via up-sampling.

Such inter-layer texture prediction may include an intra Base Layer (BL)mode, in which the reconstructed value of the reference block in thelower layer is up-sampled and the up-sampled reference block is used asthe prediction sample of the current block, and in which a residualvalue between the prediction sample and the current block is encoded,and a reference index mode, in which an up-sampled lower layer is storedin a memory and the stored lower layer is used as a reference index.

The intra-prediction of the upper layer may be performed using theintra-prediction mode information of the lower layer, wherein theintra-prediction mode of the lower layer may be referred to as a ‘BLintra mode’.

Inter-layer motion prediction is also referred to as ‘inter-layerinter-prediction’. According to the inter-layer motion prediction, thecurrent block of the upper layer may be predicted using motioninformation of the lower layer. The motion information may include amotion vector and a reference picture index.

Further, the inter-layer prediction unit 123 may perform inter-layersyntax prediction for predicting or generating the texture of thecurrent block using the syntax information of the lower layer. At thistime, the syntax information of the lower layer used for prediction ofthe current block may include information on an intra-prediction mode,motion information, etc.

Furthermore, as yet another example of inter-layer prediction,inter-layer residual prediction may be performed such that the currentblock is predicted using a differential picture, which is generatedusing differential values between the up-sampled pictures of areconstructed picture of the upper layer and a reconstructed picture ofthe lower layer.

Inter-layer texture prediction, inter-layer motion prediction,inter-layer syntax prediction, and inter-layer residual prediction havebeen described as examples of inter-layer prediction, but theinter-layer prediction applicable to the present invention is notlimited to these examples.

A residual block including residual information, which is the differencebetween the prediction block generated by each of the prediction units120 and 125 and the reconstructed block of the prediction block, isgenerated, and the residual block is input to the correspondingtransform unit 130 or 131.

Each of the transform units 130 and 131 may transform the residual blockusing a transform method such as a Discrete Cosine Transform (DCT) orDiscrete Sine Transform (DST). Whether to apply DCT or DST to transformthe residual block may be determined based on the intra-prediction modeinformation of the prediction block used to generate the residual blockand the size information of the prediction block. That is, each of thetransform units 130 and 131 may use different transform methodsdepending on the size and the prediction method of the prediction block.

Each of the quantization units 140 and 141 may quantize valuestransformed in the frequency domain by the corresponding transform units130 or 131. The quantization coefficients may change depending on thetype of block or the importance of the pictures. The value calculated bythe quantization unit 140 or 141 may be provided to theinverse-quantization unit 170 or 17 and the rearrangement unit 150 or151.

Each of the rearrangement units 150 and 151 may rearrange coefficientvalues of the quantized residual value. The rearrangement unit 150 or151 may change a 2D block format coefficient to a 1D vector formatcoefficient using a coefficient scanning method. For example, therearrangement unit 150 or 151 may change the coefficient in a 2D blockformat to coefficient in a 1D vector format by scanning coefficientsranging from a DC coefficient to a high-frequency band coefficient usinga zigzag scanning method. Depending on the size and on theintra-prediction mode of the transform block, a vertical scanning methodfor scanning 2D block format coefficients in a column direction and ahorizontal scanning method for scanning 2D block format coefficients ina row direction, rather than the zigzag scanning method, may be used.That is, the determination of which one of the zigzag scanning, verticalscanning, and horizontal scanning methods is to be used may bedetermined depending on the size and the intra-prediction mode of thetransform block.

Each of the entropy coding units 160 and 161 may perform entropy codingbased on the values calculated by the rearrangement unit 150 or 151. Theentropy coding may be implemented using, for example, various codingmethods such as Exponential Golomb, Context-Adaptive Variable LengthCoding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC).

Each of the entropy coding units 160 and 161 may be provided withvarious types of information (such as the residual coefficientinformation, block type information, prediction mode information,partition unit information, prediction block information, transmissionunit information, motion vector information, reference frameinformation, block interpolation information, and filtering informationof a coding block) from the rearrangement unit 150 or 151 and theprediction unit 120 or 125, and may perform entropy coding based on thepredetermined coding method. Further, the entropy coding unit 160 or 161may perform entropy coding on the coefficients of the coding unit inputfrom the rearrangement unit 150 or 151.

Each of the entropy coding units 160 and 161 may encode theintra-prediction mode information of the current block by binarizing theintra-prediction mode information. Each of the entropy coding units 160and 161 may include a codeword mapping unit for performing such abinarization operation, and may perform binarization in a differentmanner depending on the size of the prediction block on whichintra-prediction is to be performed. In the codeword mapping unit, acodeword mapping table may be adaptively generated using a binarizationoperation, or may be stored in advance. As another embodiment, each ofthe entropy coding units 160 and 161 may express currentintra-prediction mode information using the codeNum mapping unit forperforming codeNum mapping and the codeword mapping unit for performingcodeword mapping. In the codeNum mapping unit and the codeword mappingunit, a codeNum mapping table and a codeword mapping table may begenerated or stored.

Each of the inverse quantization units 170 and 171 and each of theinverse transform units 180 and 181 may inverse-quantize the valuesquantized by the quantization unit 140 or 141 and inverse-transform thevalues transformed by the transform unit 130 or 131. The residual valuegenerated by the inverse quantization unit 170 or 171 and the inversetransform unit 180 or 181 may be combined with the prediction blockpredicted by the motion estimation unit, the motion compensation unit,and the intra-prediction unit, which are included in the prediction unit120 or 125, and thus a reconstructed block may be generated.

Each of the filter units 190 and 191 may include at least one of adeblocking filter, an offset correction unit, and an Adaptive LoopFilter (ALF).

The deblocking filter may remove block distortion, generated due to theboundaries between blocks, in the reconstructed picture. Whether toperform deblocking, namely, whether to apply the deblocking filter tothe current block, may be determined based on the pixels included insome rows or columns of the block. When the deblocking filter is appliedto a block, a strong filter or a weak filter may be applied according tothe required strength of deblocking filtering. Also, in applying thedeblocking filter, when vertical filtering and horizontal filtering areperformed, the vertical filtering and the horizontal filtering may beprocessed in parallel.

The offset correction unit may correct an offset between the picture onwhich deblocking is performed and the original picture in pixel units.In order to perform the offset correction on a specific picture, amethod in which the pixels included in the picture are divided into acertain number of areas, the area to which an offset is to be applied isdetermined, and the offset is applied to the area may be used, or amethod in which the offset is applied in consideration of theinformation about the edge of each pixel may be used.

The Adaptive Loop Filter (ALF) may perform filtering based on a valueobtained by comparing the filtered reconstructed picture with theoriginal picture. When pixels included in the picture are divided intoone or more groups, a single filter to be applied to the correspondinggroup is determined and then filtering may be performed differentiallyfor respective groups.

Each of the filter units 190 and 191 may be implemented using only adeblocking filter, using a deblocking filter and an ALF, or using adeblocking filter and an offset correction unit, rather than using allof a deblocking filter, an ALF, and an offset correction unit.

Each of the memories 195 and 196 may store the reconstructed block orpictures calculated by the filter unit 190 or 191, and the reconstructedblock and pictures stored in the memory may be provided to theprediction unit 120 or 125 when inter-prediction is performed.

Information output from the entropy coding unit 100 b of the lower layerand information output from the entropy coding unit 100 a of the upperlayer are multiplexed by the MUX 197, and may then be output in the formof a bitstream.

The MUX 197 may be included in the encoding unit 100 b of the lowerlayer, or may be implemented as a separate device or module, unlike theencoding unit 100.

FIG. 2 is a block diagram schematically showing a decoding deviceaccording to an embodiment of the present invention.

As shown in FIG. 2, a decoding device 200 includes a decoding unit 200 aof an upper layer and a decoding unit 200 b of a lower layer.

The decoding unit 200 a of the upper layer may include an entropydecoding unit 210, a rearrangement unit 220, an inverse-quantizationunit 230, an inverse-transform unit 245, a prediction unit 250, a filterunit 260, and a memory 240.

The decoding unit 200 b of the lower layer may include an entropydecoding unit 211, a rearrangement unit 221, an inverse-quantizationunit 231, an inverse-transform unit 241, a prediction unit 251, a filterunit 261, and a memory 271.

When a bitstream including multiple layers is transmitted from theencoding device, a demultiplexer (DEMUX) 280 demultiplexes theinformation corresponding to each of the layers and then transmits theinformation to the decoding unit 200 a or 200 b of each of the layers.The input bitstream may be decoded through a process that is the reverseof the process of the encoding device.

Each of the entropy decoding units 210 and 211 may performentropy-decoding through the reverse of the entropy-coding processperformed by the entropy coding unit of the encoding device. Among thepieces of information decoded by the entropy decoding units 210 and 211,information required to generate a prediction block is provided to theprediction units 250 and 251, and a residual value, entropy-decoded bythe entropy decoding unit, may be input to the rearrangement units 220and 221.

To perform inverse transform, each of the entropy decoding units 210 and211 may use at least one of CABAC and CAVLC, like the entropy codingunits 160 and 161.

Each of the entropy decoding units 210 and 211 may decode informationabout intra-prediction and inter-prediction performed by the encodingdevice. The entropy decoding unit includes a codeword mapping unit thathas a codeword mapping table for generating an intra-prediction modenumber from a received codeword. The codeword mapping table may bestored in advance, or may be generated adaptively. When a codeNummapping table is used, a codeNum mapping unit for performing codeNummapping may be additionally included.

Each of the rearrangement units 220 and 221 may rearrange the bitstream,entropy-decoded by the entropy decoding unit 210 or 211, based on therearrangement method used by the encoding unit. The coefficients inone-dimensional vector form, may be rearranged by reconstructing theminto coefficients in 2-dimensional block-type. The rearrangement unitreceives the information about the coefficient scanning method performedby the encoding unit, and may rearrange the coefficients using a methodin which inverse scanning is performed based on the sequence of scanningperformed by the encoding unit.

Each of the inverse-quantization units 230 and 231 may perform inversequantization based on the quantization parameter provided by theencoding device and the rearranged coefficients of the block.

Each of the inverse-transform units 240 and 241 may perform inverse DCTand inverse DST, which correspond to DCT and DST performed by thecorresponding transform unit 130 or 131, on the result of quantizationperformed by the encoding device. The inverse-transform may be performedin transmission units determined by the encoding device. In thetransform unit of the encoding device, DCT and DST may be selectivelyperformed according to multiple pieces of information, such as theprediction method, the size of the current block, the predictiondirection, and the like. The inverse-transform unit 225 may performinverse transform based on the information about the transform performedby the transform unit of the encoding device. Transform may be performedbased on a coding block rather than a transform block.

Each of the prediction units 250 and 251 may generate a prediction blockbased on information about the generation of the prediction block,provided by the entropy decoding units 210 and 211, and informationabout previously decoded blocks or pictures, provided from thecorresponding memories 270 and 271.

Each of the prediction units 250 and 251 may include a prediction unitdetermination unit, an inter-prediction unit, and an intra-predictionunit.

The prediction unit determination unit receives various information,including prediction unit information input from the entropy decodingunit, prediction mode information about an intra-prediction method,motion prediction information about an inter-prediction method, and thelike, separates a prediction block from a current coding block, anddetermines whether the prediction block performs intra-prediction orinter-prediction.

The inter-prediction unit may perform inter-prediction of the currentprediction block based on information included in at least one of thepictures preceding or following the current picture, which includes thecurrent prediction block, using information required forinter-prediction of the current prediction block provided by theencoding device. In order to perform inter-prediction, it may bedetermined based on the corresponding coding block whether the motionprediction method of the prediction block included in the coding blockis a skip mode, a merge mode, or an AMVP mode.

The intra-prediction unit may generate a prediction block based oninformation about pixels in the current picture. When the predictionblock is a prediction block on which intra-prediction is performed,intra-prediction may be performed based on the intra-prediction modeinformation about the prediction block, provided by the encoding device.The intra-prediction unit may include an MDIS filter for performingfiltering on reference pixels of the current block, a reference pixelinterpolation unit interpolating reference pixels for generatingreference pixels in a pixel unit smaller than an integer pixel, and a DCfilter for generating a prediction block through filtering when theprediction mode of the current block is a DC mode.

The prediction unit 250 of the decoding unit 200 a of the upper layermay further include an inter-layer prediction unit for performinginter-layer prediction, in which the upper layer is predicted usinginformation about the lower layer.

The inter-layer prediction unit may perform inter-layer textureprediction, inter-layer inter-prediction, inter-layer syntax prediction,etc. using the texture information, intra-prediction mode information,motion information, syntax information, etc. of the lower layer.

Prediction that uses the texture of a reference block in the lower layeras the predicted value of the current block in the upper layer accordingto the inter-layer texture prediction may be performed. The texture ofthe reference block may be scaled via up-sampling.

Inter-layer texture prediction includes an intra BL mode, in which thereconstructed value of the reference block in the lower layer isup-sampled and the up-sampled reference block is used as a predictedvalue for the current block, and in which a residual value between thepredicted value and the current block is encoded, and a reference indexmode, in which an up-sampled base layer is stored in the memory and thestored base layer is used as a reference index.

The intra-prediction of the upper layer may be performed using theintra-prediction mode information of the lower layer, wherein theintra-prediction mode of the lower layer may be called a ‘BL intramode’.

According to the inter-layer motion prediction, the current block of theupper layer may be predicted using the motion information of the lowerlayer.

Further, the inter-layer prediction unit may perform inter-layer syntaxprediction for predicting or generating the texture of a current blockusing the syntax information of the lower layer. Here, the syntaxinformation of the lower layer used for the prediction of the currentblock may include information about an intra-prediction mode, motioninformation, etc.

Furthermore, the inter-layer prediction unit may perform inter-layerresidual prediction for predicting the current block using adifferential picture that is generated using differential values betweenup-sampled pictures of the reconstructed picture of the upper layer andthe reconstructed picture of the lower layer.

Inter-layer texture prediction, inter-layer inter-prediction,inter-layer syntax prediction, and inter-layer residual prediction havebeen described as examples of inter-layer prediction, but theinter-layer prediction applicable to the present invention is notlimited to those examples.

The reconstructed blocks or pictures may be provided to the filter units260 and 261. Each of the filter units 260 and 261 may include adeblocking filter, an offset correction unit, and an ALF.

The encoding device may provide information about whether a deblockingfilter has been applied to the corresponding block or picture andinformation indicating that the applied filter is a strong filter or aweak filter when the deblocking filter is applied. The deblocking filterof the decoding device receives information about the deblocking filterprovided by the encoding device, and the decoding device may performdeblocking filtering on the corresponding block.

The offset correction unit may perform offset correction on thereconstructed picture based on the type of offset correction applied tothe picture during encoding and information about the offset value.

The adaptive loop filter (ALF) may perform filtering based on the valueobtained by comparing the picture, reconstructed after filtering, withthe original picture. The ALF may be applied to a coding unit based oninformation about whether to apply the ALF, information about ALFcoefficients, etc., which are provided from the encoding device. SuchALF information may be provided, with the ALF information being includedin a specific parameter set.

Each of the memories 270 and 271 may store the reconstructed picture orblock to be used as a reference picture or a reference block, and mayoutput the reconstructed picture.

The encoding device and decoding device may perform encoding on three ormore layers rather than two layers, in which case the encoding unit ofthe upper layer and the decoding unit of the upper layer may includemultiple encoding units and decoding units, corresponding in number tothe number of upper layers.

Hereinafter, although, in the embodiments of the present invention, acoding unit has been described using the term “coding block” for theconvenience of description, it may be a block on which decoding as wellas encoding is performed. Below, a reference picture list generationmethod, which is described with reference to the drawings based on theembodiments of the present invention, may be implemented to suit thefunctions of respective modules described above with reference to FIGS.1 and 2. The encoding device and the decoding device may also beincluded in the scope of the present invention.

As described above, in the coding of video that supports a multi-layerstructure, there are a method for encoding/decoding an enhancement layerusing the motion information and the texture information of a base layerand a method for encoding/decoding an enhancement layer using anup-sampled base layer as a reference picture without changing a decodingmethod based on the coding unit (CU) or the prediction unit (PU) of abase layer. The latter method may be referred to as a ‘reference pictureindex (RefIdx) mode’.

When the reference picture index (RefIdx) mode is used, a picture thathas been previously decoded in the enhancement layer may be used as areference picture or, alternatively, a picture in the base layer or thelower layer may be up-sampled and then used as a reference picture.

Hereinafter, in the present invention, when a picture in the base layeror the lower layer is up-sampled and used as a reference picture, theup-sampled base layer picture or lower layer picture is referred to asan ‘inter-layer reference picture’.

Even in video that supports a multi-layer structure for multiple views,inter-prediction may be performed by using a layer for another view,other than the current layer, as a reference picture. The layer foranother view, which is referred to for the encoding and decoding of thecorresponding layer, may also be referred to as an ‘inter-layerreference picture’.

That is, when the reference picture set of the enhancement layer isconfigured to code video having a multi-layer structure that supportsscalability, rather than a single layer, an inter-layer referencepicture must also be taken into consideration.

Typically, inter-prediction may be performed such that at least one ofthe previous picture and the subsequent picture, relative to the currentpicture, is used as a reference picture, and prediction of the currentblock is performed based on the reference picture. A picture used forthe prediction of the current block is referred to as a ‘referencepicture’ or ‘a reference frame’.

The reference picture is specified by a reference picture index(refIdx), and a predetermined region in the reference picture isspecified as a reference block via a motion vector.

In inter-prediction, a prediction block for the current block may begenerated by selecting a reference picture and a reference blockcorresponding to the current block in the reference picture.

In inter-prediction, the encoding device and the decoding device mayderive the motion information of the current block, and may then performinter-prediction and/or motion compensation based on the derived motioninformation. Here, the encoding device and the decoding device mayimprove encoding/decoding efficiency by utilizing the motion informationof a reconstructed neighboring block and/or a collocated block (colblock), corresponding to the current block, in a previouslyreconstructed collocated (col) picture.

Here, the reconstructed neighboring block is a block in the currentpicture that has been encoded and/or decoded and reconstructed, and mayinclude a block adjacent to the current block and/or a block located atthe external corner of the current block. Further, the encoding deviceand the decoding device may determine a predetermined relative location,based on the block that is present at the location spatiallycorresponding to the current block, in the col picture, and may derivethe col block based on the determined relative position (position insideand/or outside of the block located at the position spatiallycorresponding to the current block). Here, for example, the col picturemay correspond to one of the reference pictures included in a referencepicture list.

The inter-prediction may generate a prediction block so that a residualsignal between the prediction block and the current block is minimizedand the size of a motion vector is also minimized.

Meanwhile, a scheme for deriving motion information may differ accordingto the prediction mode for the current block. The prediction modeapplied for the inter-prediction may include an Advanced Motion VectorPredictor (AMVP) mode, a merge mode, etc.

For example, when the AMVP mode is applied, each of the encoding deviceand the decoding device may generate a motion vector candidate listusing the motion vector of a reconstructed neighboring block and/or themotion vector of a col block. The motion vector of the reconstructedneighboring block and/or the motion vector of the col block may be usedas motion vector candidates. The encoding device may transmit apredicted motion vector index, which indicates an optimal motion vectorselected from among the motion vector candidates included in the list tothe decoding device. Here, the decoding device may select a predictedmotion vector of the current block from among the motion vectorcandidates included in the motion vector candidate list using the motionvector index.

The encoding device may obtain a Motion Vector Difference (MVD) betweenthe motion vector of the current block and the predicted motion vector,encode the MVD, and transmit the encoded MVD to the decoding device.Here, the decoding device may decode the received MVD and derive themotion vector of the current block using the sum of the decoded MVD andthe predicted motion vector.

The encoding device may also transmit a reference picture index,indicating a reference picture, or the like to the decoding device.

The decoding device may predict the motion vector of the current blockusing pieces of motion information of the neighboring blocks, and mayderive the motion vector of the current block using a residual receivedfrom the encoding device. The decoding device may generate a predictionblock for the current block based both on the derived motion vector andon the reference picture index information received from the encodingdevice.

As another example, when the merge mode is applied, the encoding deviceand the decoding device may generate a merge candidate list using boththe motion information of a reconstructed neighboring block and/or themotion information of a collocated (col) block. That is, when the motioninformation of the reconstructed neighboring block and/or the col blockis present, the encoding device and the decoding device may use themotion information as a merge candidate for the current block.

The encoding device may select a merge candidate that enables optimalencoding efficiency to be provided, from among merge candidates includedin the merge candidate list, as the motion information of the currentblock. Here, the merge index that indicates the selected merge candidatemay be transmitted to the decoding device, with the merge index beingincluded in a bitstream. The decoding device may select one from amongthe merge candidates included in the merge candidate list using thetransmitted merge index, and may determine the selected merge candidateto be the motion information of the current block. Therefore, when themerge mode is applied, the motion information of the reconstructedneighboring block and/or the col block may be used as the motioninformation of the current block without change. The decoding device mayreconstruct the current block by adding the prediction block to theresidual transmitted from the encoding device.

In the above-described AMVP and merge modes, in order to derive themotion information of the current block, the motion information of thereconstructed neighboring block and/or the motion information of the colblock may be used.

In the skip mode, which is one of the other modes used forinter-prediction, information about a neighboring block may be used forthe current block, without change. Therefore, in the skip mode, theencoding device transmits no syntax information, such as a residual,except the information indicating the block, the motion information ofwhich is to be used as the motion information of the current block, tothe decoding device.

The encoding device and the decoding device may generate the predictionblock for the current block by performing motion compensation on thecurrent block based on the derived motion information. Here, theprediction block may mean a motion-compensated block generated as theresult of performing motion compensation on the current block. Further,multiple motion-compensated blocks may constitute a singlemotion-compensated picture.

The decoding device may check a skip flag, a merge flag, etc. receivedfrom the encoding device, and may derive motion information required forinter-prediction of the current block, for example, information about amotion vector, a reference picture index, etc., in accordance with thechecked flags.

The processing unit on which prediction is performed and the processingunit on which a prediction method and detailed content are designatedmay differ from each other. For example, the unit of a prediction modemay be designated as a prediction block, and then prediction may beperformed on a transform block basis. Alternatively, the unit of theprediction mode may be designated as a prediction block, andintra-prediction may be performed on a transform block basis.

Pictures encoded/decoded prior to the current picture are stored inmemory (e.g. Decoded Picture Buffer: DPB) and may then be used for theprediction of a current block (a current picture). A list of picturesusable for the inter-prediction of the current block is maintained as areference picture list.

P slice denotes a slice decoded via intra-prediction, orinter-prediction that uses a maximum of one motion vector and onereference picture. B slice denotes a slice decoded via intra-predictionor inter-prediction that uses a maximum of two motion vectors and tworeference pictures. Here, the reference pictures include short-termreference pictures and long-term reference pictures. The pictures may bespecified by a Picture Order Count (POC), indicating the sequence ofindication, wherein it can be seen that short-term reference picturesare pictures, the POC of which is not greatly different from that of thecurrent block, and the long-term reference pictures are pictures, thePOC of which is greatly different from that of the current picture.

Reference picture list 0 (for the convenience of description,hereinafter referred to as ‘L0’) is a list of reference pictures usedfor inter-prediction of a P slice or a B slice. Reference picture list 1(for the convenience of description, hereinafter referred to as ‘L1’) isused for the inter-prediction of a B slice. Therefore, L0 is used forinter-prediction of blocks in a P slice for performing unidirectionalprediction, and L0 and L1 are used for inter-prediction of blocks in a Bslice for performing bidirectional prediction.

The decoding device constructs a reference picture list when performingdecoding on a P slice and a B slice via inter-prediction. Referencepictures used for inter-prediction are designated via the referencepicture list. A reference picture index is an index indicating eachreference picture on the reference picture list.

The reference picture list may be constructed based on reference picturesets transmitted from the encoding device. Such a reference picture setmay be composed of the POC of pictures used as reference pictures and aflag (used_by_curr_pic_s0_flag) indicating whether the correspondingpicture is directly referred to. The reference pictures used toconstruct the reference picture list may be stored in memory (e.g. DPB).The pictures stored in the memory (pictures encoded/decoded prior to thecurrent picture) are managed by the encoding device and the decodingdevice.

FIG. 3 is a conceptual diagram showing an example of a reference pictureset that includes short-term reference pictures.

As shown in the drawing, a reference picture set (RPS) may comprise thePOC of each of short-term reference pictures that must be stored in theDPB at the current time, and flag information indicating whether thecurrent picture directly refers to a specific picture.

For example, when inter-prediction of a picture having a POC of 21 isperformed, a total of three pictures (pictures having POC of 20, 19, and16) as short-term reference pictures may be referred to, and all of thethree pictures have a value of 1 as ‘used_by_curr_pic_s0_flag’, and thusthe pictures are directly used for prediction of the picture having aPOC of 21.

Meanwhile, when inter-prediction of a picture having a POC of 26 isperformed, a total of three pictures (having a POC of 25, 24, and 20) asshort-term reference pictures may be referred to, but the‘used_by_curr_pic_s0_flag’ value of the picture having a POC of 25 is 0,unlike the ‘used_by_curr_pic_s0_flag’ values of the pictures having POCsof 24 and 20. In this case, the picture having a POC of 25 is notdirectly used for inter-prediction of the picture having a POC of 26.

Among current pictures, pictures that do not appear in the referencepicture set are marked with an ‘unused for reference’ indicator,indicating that the pictures are not used as reference pictures, and maybe deleted from the DPB.

FIG. 4 is a conceptual diagram showing a method for deriving the POC oflong-term reference pictures.

As shown in the drawing, since a long-term reference picture has a POCgreatly differing from that of the current picture, it may berepresented using the Least Significant Bit (LSB) and the MostSignificant Bit (MSB) of the POC.

‘MaxPocLsb’ denotes the maximum value that may be represented by LSB.When MaxPocLsb is 32, a long-term reference picture (LTRP) having a POCof 84 may be represented by 32*2+20, where LSB is 20 and MSB is 2.

The current picture having a POC of 338 may be represented by 32*10+11when the maximum value that may be represented by LSB is 32, and thus 10is the value of MSB and 11 is the value of LSB.

‘delta_poc_msb_cycle_lt’ denotes the value required to determine‘DeltaPocMsbCycleLt’ that is the MSB of POC in the long-term referencepicture set of the current picture. ‘DeltaPocMsbCycleLt’ may correspondto the difference between the MSB of the POC of the current picture andthe MSB of the POC of the reference picture.

In the case of the long-term reference picture, the POC of the referencepicture may be derived using the LSB value of the POC of the referencepicture and the difference between the MSB of the POC of the currentpicture and the MSB of the POC of the reference picture.

For example, when the POC of the current picture is 331, a long-termreference picture (LTRP[0]) having a POC of 308 and indexed with ‘0’ maybe represented by 331−1*32−11+20 if both the LSB value of 20 of thelong-term reference picture and the difference of 1 between the MSB ofthe POC of the current picture and the MSB of the POC of the referencepicture are used.

Similarly, the long-term reference picture (LTRP[1]) that is indexedwith ‘1’ and has a POC of 170 may be represented by 331−5*32−11+10 ifboth the LSB of 10 of the long-term reference picture and the differenceof 5 between the MSB of the POC of the current picture and the MSB ofthe POC of the reference picture are used.

As shown in FIGS. 3 and 4, an initial reference picture list that can bereferred to by the current picture may be constructed using the list ofpictures present in the short-term reference picture buffer and thelong-term reference picture buffer.

FIG. 5 is a diagram showing an example in which a reference picture listis constructed.

The reference pictures may be classified into a first short-termreference picture set (RefPicSetStCurr0) composed of reference picturesRef1 and Ref2 having a POC less than that of a current picture (Curr)based on the current picture, a second short-term reference picture set(RefPicSetStCurr1) composed of reference pictures Ref3 and Ref4 having aPOC greater than that of the current picture, and a long-term referencepicture set (RefPicSetLtCurr) composed of long-term reference picturesRef LT1 and Ref LT2.

In this case, the first short-term reference picture set(RefPicSetStCurr0) is composed of pictures having a flag value(used_by_curr_pic_s0_flag) of 1 (delta_poc_s0 withused_by_curr_pic_s0_flag=1), and the second short-term reference pictureset (RefPicSetStCurr1) is also composed of pictures having a flag value(used_by_curr_pic_s1_flag) of 1 (delta_poc_s1 withused_by_curr_pic_s1_flag=1).

As an aggregation of reference picture sets having different propertiesin this way, an initial reference picture list may be constructed.

As shown in FIG. 5, reference picture list 0, that is, L0, isconstructed in the sequence of the first short-term reference pictureset (RefPicSetStCurr0), the second short-term reference picture set(RefPicSetStCurr1), and the long-term reference picture set(RefPicSetLtCurr).

Meanwhile, reference picture list 1, that is, L1, is constructed in thesequence of the second short-term reference picture set(RefPicSetStCurr1), the first short-term reference picture set(RefPicSetStCurr0), and the long-term reference picture set(RefPicSetLtCurr).

The number of reference pictures that may be included in the referencepicture list may be determined based on the information transmitted fromthe encoding device. For example, after constructing the referencepicture lists, the encoding device may determine the number of referencepictures to be used, and may transmit information about the number ofreference pictures to be used (e.g.num_ref_idx_lX_default_active_minus1, X=0 or 1) to the decoding deviceas the syntax element of a sequence parameter set (SPS). The decodingdevice may use the number of reference pictures, which is specified asthe value obtained by adding 1 to the received information(num_ref_idx_lX_default_active_minus1), as a default value in a currentsequence.

Further, when desiring to designate the number of reference pictures foreach picture or each slice, the encoding device may transmit separateinformation indicating the number of reference pictures (e.g.num_ref_idx_l1_active_minus1, X=0 or 1) via a picture parameter set(PPS), a slice header, or the like. The decoding device may use a value,specified as the value obtained by adding 1 to the received information(num_ref_idx_l1_active_minus1), as the number of reference pictures inthe current picture or the current slice.

When inter-prediction is performed, motion compensation may be performedusing the reference pictures specified in the reference picture listconstructed as described above.

In a multi-layer structure that provides spatial scalability ormultiview scalability, the reference pictures of the enhancement layermay include reference pictures in the same layer and inter-layerreference pictures.

In this case, signaling of the inter-layer reference pictures may beperformed using information required to identify layers and informationrequired to identify reference pictures. For example, if the value ofnuh_layer_id, which is present in an access unit identical to thecurrent picture in an i-th layer and which is a j-th layer identifier(where i>j) transmitted with the layer identifier being included in theNetwork Abstraction Layer (NAL) unit header, is identical to theRefPiclayerId of the current picture, the corresponding picture may bedetermined to be used as the reference picture for the current picture.The inter-layer reference pictures may be indicated by long-termreference pictures.

‘RefPicLayerId’ denotes a value that can be signaled with the syntaxelement inter_layer_pred_layer_idc included in a slice header, and meansa layer referred to by the current layer for inter-layer prediction.

FIG. 6 is a conceptual diagram showing an example in which aninter-layer reference picture list is constructed according to anembodiment of the present invention.

As shown in FIG. 6, in video having a multi-layer structure, an initialreference picture list may be constructed using a short-term referencepicture set (RefPicSetStCurrBefore[i], hereinafter referred to as a‘first reference picture set’) composed of short-term reference pictureshaving POCs less than that of a current picture, a short-term referencepicture set (RefPicSetStCurr After[i], hereinafter referred to as a‘second reference picture set’) composed of short-term referencepictures having POCs greater than that of the current picture, along-term reference picture set (RefPicSetLtCurr[i], hereinafterreferred to as a ‘third reference picture set’), and an inter-layerreference picture set (RefPicSetILCurr[i], hereinafter referred to as a‘fourth reference picture set’).

The reference pictures included in the fourth reference picture set maybe the pictures of a layer supporting spatial scalability, picturesincluded in a layer supporting multiview scalability, or pictures of alayer supporting depth scalability or video quality scalability. Here,the spatial scalability and video quality scalability may be coded inthe same codec structure.

When a bitstream supports two or more scalability types, referencepictures for respective scalability types may be integrated into asingle reference picture set. When a single reference picture set isconfigured for multiple scalability types, information about thesequence of the scalability types aligned in the reference picture setmay be transmitted from the encoding device to the decoding device.

Meanwhile, reference pictures sets may be individually configured formultiple scalability types. That is, for a current picture, a fourthreference picture set, a fifth reference picture set, and a sixthreference picture set, each composed of inter-layer reference pictures,may be generated in addition to a first reference picture set, a secondreference picture set, and a third reference picture set. Such aninter-layer reference picture set may be adaptively added to thereference picture list depending on the frequency of occurrence. Forexample, a reference picture set having high occurrence frequency may beallocated to the low index of the reference picture list.

The initial reference picture list of FIG. 6 is L0 in which the firstreference picture set is configured in the lowest sequential position ofthe list. At this time, the fourth reference picture set may be added tothe last sequential position of the initial reference picture list L0.

The initial reference picture list 0 is constructed using pictureshaving flag information (used_by_curr_pic_flag) of 1 among the referencepictures included in the respective reference picture sets, wherein theflag information indicates whether the corresponding picture iscurrently used as the reference picture. As shown in the drawing, theinitial reference picture list 0 may be constructed using only first andsecond pictures among four pictures included in each reference pictureset.

The initial reference picture list may be modified for each picture oreach slice, and reference pictures may be changed based on themodification. The initial reference picture list may be modified usingsyntax elements included in a slice header (e.g.ref_pic_list_modification_flag_l0, list_entry_l0,ref_pic_list_modification_flag_l1, list_entry_l1).

The ref_pic_list_modification_flag_l0 andref_pic_list_modification_flag_l1 may explicitly indicate whetherreference pictures are transmitted from the encoding device to thedecoding device, in the reference picture list 0 and the referencepicture list 1. When the flag value is 1, the reference picture list isexplicitly specified using information about transmitted referencepictures, whereas when the flag value is 0, the reference picture listis implicitly derived as the initial reference picture set.

When the flag value is 1, list_entry_l0 denotes information aboutdetailed entries, that is, the index of reference pictures, constitutinga reference picture list for L0, and list_entry_l1 denotes informationabout detailed entries constituting a reference picture list for L1.

By means of this modification, final reference picture list 0 may beconstructed using first and second reference pictures (0, 1) of thefirst reference picture set, first and second reference pictures (0, 1)of the second reference picture set, and the first reference picture (0)of the fourth reference picture set.

In accordance with another example of the present invention, uponconstructing the reference picture list, the fourth reference pictureset for the inter-layer reference picture may be arranged at asequential position other than the last sequential position in the listof FIG. 6. In the multi-layer structure, a strong correlation is presentbetween the enhancement layer and the base layer due to thecharacteristics of video, and thus there may frequently occur the casewhere inter-layer reference pictures are referred to. When aninter-layer reference picture having a high occurrence frequency isadded to the position other than the last position of the referencepicture list, the encoding performance of the reference picture list maybe improved.

In consideration of this fact, an inter-layer reference picture may beadded to various positions of a reference picture list. FIGS. 7 to 10are conceptual diagrams showing examples in which an inter-layerreference picture list is constructed according to embodiments of thepresent invention.

FIG. 7 illustrates the configuration of reference picture list 0according to an embodiment of the present invention, wherein theconfiguration of reference picture list 0 is illustrated. As illustratedin the drawing, a fourth reference picture set that is an inter-layerreference picture set may be aligned at the second sequential positionof a reference picture list.

Reference picture list 0 is constructed in the sequence of a firstreference picture set, a fourth reference picture set, a secondreference picture set, and a third reference picture set.

Reference picture list 0 is composed of pictures having flag information(used_by_curr_pic_flag) of 1, among reference pictures included inrespective reference picture sets, wherein the flag informationindicates whether the corresponding pictures are currently used asreference pictures. As shown in the drawing, initial reference picturelist 0 may be constructed using only first and second pictures of fourpictures in each of the reference picture sets.

The initial reference picture list constructed in this way may bemodified for each picture or slice, and the entries of referencepictures may be changed according to the modification.

By means of this modification, final reference picture list 0 may beconstructed using first and second reference pictures (0, 1) of thefirst reference picture set, first and second reference pictures (0, 1)of the fourth reference picture set, and the first reference picture (0)of the second reference picture set.

FIG. 8 is a diagram showing the configuration of reference picture list0 according to another embodiment of the present invention.

As shown in FIG. 8 <a>, reference picture list 0 may be constructed inthe sequence of a first reference picture set composed of short-termreference pictures having POCs less than that of a current picture, asecond reference picture set composed of short-term reference pictureshaving POCs greater than that of the current picture, a fourth referencepicture set composed of inter-layer reference pictures, and a thirdreference picture set composed of long-term reference pictures.

Alternatively, as shown in FIG. 8 <b>, reference picture list 0 isconstructed such that the fourth reference picture set composed ofinter-layer reference pictures is arranged at a first sequentialposition, and then the first reference picture set composed ofshort-term reference pictures having POCs less than that of the currentpicture, the second reference picture set composed of short-termreference pictures having POCs greater than that of the current picture,and the third reference picture set composed of long-term referencepictures are sequentially arranged.

In <b>, there is an advantage in that, when the frequency at whichinter-layer reference pictures are referred to is high, the encoding anddecoding efficiency of the reference picture list may be improved.

Alternatively, in a further embodiment, similar to the generation of thereference picture list of a single layer, the reference picture list maybe constructed in the sequence of a first reference picture set composedof short-term reference pictures having POCs less than that of thecurrent picture, a second reference picture set composed of short-termreference pictures having POCs greater than that of the current picture,and a third reference picture set composed of long-term referencepictures, and thereafter the positions to which inter-layer referencepictures are to be added may be specified at a slice or sequence level,that is, in a slice header or sequence parameter header.

The inter-layer reference pictures may be added to the specifiedpositions, and then the reference picture list may be constructed. Suchsignaling information may be encoded with the signaling informationbeing included in the slice header, sequence header or video parameterset, and may be transmitted to the decoding device.

FIG. 9 illustrates the construction of reference picture list 1according to an embodiment of the present invention. As shown in thedrawing, a fourth reference picture set that is an inter-layer referencepicture set may be aligned at the last sequential position of thereference picture list.

Reference picture list 1 is constructed in the sequence of a secondreference picture set, a first reference picture set, a third referencepicture set, and the fourth reference picture set.

Reference picture list 1 is constructed using pictures having flaginformation (used_by_curr_pic_flag) of 1, among reference picturesincluded in respective reference picture sets, wherein the flaginformation indicates whether the corresponding pictures are currentlyused as reference pictures. As shown in the drawing, initial referencepicture list 1 may be constructed using only first and second picturesof four pictures included in each of the reference picture sets.

The initial reference picture list constructed in this way may bemodified for each picture or slice, and the entries of the referencepictures may be changed according to the modification.

By means of this modification, final reference picture list 1 may beconstructed using the first reference picture (0) of the secondreference picture set, the first and second reference pictures (0, 1) ofthe first reference picture set, and the first and second referencepictures (0, 1) of the fourth reference picture set.

FIG. 10 is a diagram showing the configuration of reference picture list1 according to another embodiment of the present invention.

As shown in FIG. 10 <a>, reference picture list 1 may be constructed inthe sequence of a second reference picture set composed of short-termreference pictures having POCs greater than that of a current picture, afirst reference picture set composed of short-term reference pictureshaving POCs less than that of the current picture, a fourth referencepicture set composed of inter-layer reference pictures, and a thirdreference picture set composed of long-term reference pictures.

Alternatively, as shown in FIG. 10 <b>, reference picture list 1 may beconstructed such that the second reference picture set composed ofshort-term reference pictures having POCs greater than that of thecurrent picture is allocated to a first sequential position, and thefourth reference picture set composed of inter-layer reference picturesis allocated to a second sequential position. Then, the referencepicture list 1 may be constructed in the sequence of the first referencepicture set composed of short-term reference pictures having POCs lessthan that of the current picture, and the third reference picture setcomposed of long-term reference pictures.

Alternatively, similar to the generation of the reference picture listof a single layer, the reference picture list may be constructed in thesequence of the second first reference picture set composed ofshort-term reference pictures having POCs greater than that of thecurrent picture, the first reference picture set composed of short-termreference pictures having POCs less than that of the current picture,and the third reference picture set composed of long-term referencepictures, and then positions to which inter-layer reference pictures areto be added may be specified at a slice or sequence level, that is, in aslice header or sequence parameter header.

The inter-layer reference pictures may be added to the specifiedpositions, and then the reference picture list may be constructed. Suchsignaling information may be encoded with the signaling informationbeing included in the slice header, sequence header or video parameterset, and may be transmitted to the decoding device.

In accordance with a further embodiment of the present invention, thealignment sequence of an inter-layer reference picture set may be setaccording to the index (tempralId) of a temporal sub-layer for thecurrent picture.

FIG. 11 illustrates a reference picture list constructed using the indexof a temporal sub-layer according to an embodiment of the presentinvention.

In a multi-layer structure, the frequency at which an inter-layerreference picture is used may differ depending on the temporal sub-layerfor a current picture belonging to an enhancement layer. As temporalIDthat is the index value of a temporal sub-layer is larger, it may bemore effective to perform inter-prediction by referring to pictures inthe same layer rather than by referring to reference pictures in anotherlayer.

In other words, when the value of tempralId is smaller, it may be moreeffective in coding to refer to inter-layer pictures rather thanreferring to pictures in the same layer. When the value of tempralId islarger, it may be more efficient in coding to use pictures in the samelayer as reference pictures rather than using inter-layer pictures asreference pictures.

In the present embodiment, the positions to which inter-layer referencepictures are to be added in an initial reference picture list may beadaptively changed according to the index (tempralId) of a temporalsub-layer in consideration of the fact that the frequency at whichinter-layer pictures are referred to is varied according to the temporalsub-layer.

FIG. 11 is a diagram showing the construction of reference picture list0 when the values of tempralId range from 0 to 2.

When the value of tempralId is 0, there is a strong possibility thatinter-layer prediction will be performed in the enhancement layer, andthus a fourth reference picture set composed of inter-layer referencepictures may be added to the first sequential position of an initialreference picture list.

The initial reference picture list constructed using pictures, for whichflag information (used_by_curr_pic_flag) indicating whether thecorresponding picture is currently used as a reference picture is 1,among reference pictures included in respective reference picture sets,is composed of four pictures (0, 1, 2, 3) included in a fourth referencepicture set, and first and second pictures (0,1) of each of a firstreference picture set, a second reference picture set, and a thirdreference picture set.

As shown in the drawing, after the initial values of the referencepicture list have been set, the reference picture list is modified, andthen a final reference picture list may be set. Information about themodification of the reference picture list may be signaled in a sliceheader.

The modified final reference picture list 0 is constructed in thesequence of first and second pictures (0,1) of the first referencepicture set, first and second pictures (0,1) of the fourth referencepicture set, and the first picture (0) of the second reference pictureset.

When the value of tempralId is 1, the fourth reference picture setcomposed of inter-layer reference pictures may be added subsequent tothe first reference picture set in the initial reference picture list 0.

The initial reference picture list constructed using pictures, for whichflag information (used_by_curr_pic_flag) indicating whether thecorresponding picture is currently used as a reference picture is 1, iscomposed of first and second pictures (0,1) of each of the firstreference picture set, the fourth reference picture set, the secondreference picture set, and the third reference picture set.

The modified final reference picture list 0 is constructed in thesequence of first and second pictures (0,1) of the first referencepicture set, first and second pictures (0,1) of the fourth referencepicture set, and the first picture of the second reference picture set.

When the value of tempralId is 2, there is a strong possibility thatinter-prediction in the same layer will be performed rather thaninter-layer prediction in an enhancement layer, and thus the fourthreference picture set composed of inter-layer reference pictures may beadded subsequent to the third reference picture set, that is, at thelast sequential position, in the initial reference picture list.

Initial reference picture list 0 constructed using pictures, for whichflag information (used_by_curr_pic_flag) indicating whether thecorresponding picture is currently used as a reference picture is 1, iscomposed of first and second pictures (0,1) of each of a first referencepicture set, a second reference picture set, a third reference pictureset, and a fourth reference picture set.

The modified final reference picture list is constructed in the sequenceof first and second pictures (0,1) of the first reference picture set,the first and second pictures (0,1) of the second reference picture set,and the first picture (0) of the fourth reference picture set.

Similar to the above description, the initial reference list L1 may beconfigured such that the position at which the fourth reference pictureset is to be added varies according to the value of temporalId. Forexample, when the value of temporalId is 0, initial reference list L1may be constructed in the sequence of the fourth reference picture set,the second reference picture set, the first reference picture set, andthe third reference picture set. When the value of temporalId is 1, theinitial reference list L1 may be constructed in the sequence of thesecond reference picture set, the fourth reference picture set, thefirst reference picture set, and the third reference picture set. Whenthe value of temporalId is as large as 2, the fourth reference pictureset may be added to the last sequential position of the initialreference picture list L1.

In summary, as shown in FIG. 11, the position, to which inter-layerreference pictures are to be added, in the initial reference picturelist, may be adaptively changed according to the value of temporalId ofthe current picture.

Meanwhile, when a current picture refers to multiple layers, that is,when there are multiple inter-layer reference pictures, the multiplereference pictures may be separated to be capable of configuringmultiple inter-layer reference picture sets. The multiple inter-layerreference picture sets may be aligned at different sequential positionsin an initial reference picture list.

For example, in video supporting multiview scalability, when multipleviews, that is, multiple layers, are used as reference pictures, afourth reference picture set composed of inter-layer reference picturesmay be separated and included in the reference picture list. Thereference picture list may be constructed using various methodsdepending on the sequence of views of the current layer and the layer ofthe reference picture or the degree of proximity of views thereof.

A layer having a smaller difference in view from the current layer has astrong possibility that pictures in the corresponding layer will be usedas inter-layer reference pictures. In other words, a layer having alarger difference in view from the current layer has a weak possibilitythat pictures in the corresponding layer will be referred to by thecurrent picture. In accordance with the present embodiment, the sequencein which reference pictures are added to the reference picture list maybe adaptively modified depending on the proximity sequence in which thefrequency of occurrence of the reference pictures, that is, the degreeof reference of pictures between views, is taken into consideration.That is, the position to which inter-layer reference pictures are to beadded in the reference picture list may be adaptively determineddepending on the number of inter-layer reference pictures and thesequence of the inter-layer reference pictures.

That is, a lower index in a reference picture list may be allocated to areference picture in a layer having a smaller difference in view fromthe current layer, and a higher index in the reference picture list maybe allocated to a reference picture in a layer having a largerdifference in view from the current layer.

FIG. 12 illustrates a reference picture list constructed using multiviewreference pictures according to an embodiment of the present invention.

As shown in FIG. 12, among reference picture 0, reference picture 1,reference picture 2, and reference picture 3 that may be included in amultiview reference picture set, the reference picture 0 and thereference picture 1 may be aligned at the first position of referencepicture list 0, and the reference picture 2 and the reference picture 3may be aligned subsequent to a first reference picture set composed ofshort-term reference pictures.

Here, the reference picture 0 and the reference picture 1 may bereference pictures in a layer having a smaller difference in view fromthe current layer, and the reference picture 2 and the reference picture3 may be pictures having a larger difference in view from the currentlayer.

As another example, reference picture 0 that is a first inter-layerreference picture may be aligned at the first sequential position of theinitial reference picture list, reference picture 1 that is a secondinter-layer reference picture may be aligned subsequent to the firstreference picture set composed of short-term reference pictures, andsubsequent inter-layer reference pictures may be sequentially added tothe position subsequent to a long-term reference picture set composed oflong-term reference pictures.

The difference in view between the current layer and the reference layerwhich can be aligned in a fore portion of the reference picture list maybe set to a default value, or may be variably set by the encoding deviceand transmitted to the decoding device.

Further, when an inter-layer reference picture set is added to aninitial reference picture list, information about criterion of applyingthe position of addition differently, may be set to a fixed value andthe information may be signaled to the decoding device, with beingincluded in a video parameter set (VPS).

In reference picture list 1, a reference picture in a layer having asmaller difference in view from the current layer may be aligned at thefirst position of an initial reference picture list, and may be alignedsubsequent to a second reference picture set composed of short-termreference pictures having POCs greater than that of the current picture.A reference picture set composed of reference pictures having a largerdifference in view from the current layer may be aligned at the lastposition of the initial reference picture list or may be aligned at asequential position prior to a third reference picture set composed oflong-term reference pictures.

Alternatively, reference pictures in a layer having a larger differencein view from the current layer may be aligned at the first position ofthe initial reference picture list, or may be aligned subsequent to asecond reference picture set composed of short-term reference pictureshaving POCs greater than that of the current picture. Further, areference picture set composed of reference pictures having a smallerdifference in view from the current layer may be aligned at the lastposition of the initial reference picture list or aligned at asequential position prior to a third reference picture set composed oflong-term reference pictures.

Although multiview reference points have been included in theinter-layer reference picture set of FIG. 12, the construction of thereference picture list shown in FIG. 12 may also be applied to the casewhere the type of scalability is spatial scalability and pictures ofmultiple layers are used as reference pictures. That is, referencepictures may be separated and added to the reference picture listdepending on the difference between the IDs (dependency IDs) required toidentify the current picture and spatial layers.

As described above, when an inter-layer reference picture set isincluded in a reference picture list, the position to which theinter-layer reference picture set is to be added may be variously set,and the method for signaling this position may include multiple methods.

FIG. 13 is a diagram showing a method for generating a reference picturelist according to an embodiment of the present invention.

First, the decoding device generates a short-term reference picture setand a long-term reference picture set composed of pictures present inthe same layer as a current picture (S1310).

The short-term reference picture set may include a short-term referencepicture set composed of short-term reference pictures having POCs lessthan that of the current picture, and a short-term reference picture setcomposed of short-term reference pictures having POCs greater than thatof the current picture.

The long-term reference picture set is composed of long-term referencepictures having a large difference in POC from that of the currentpicture.

Initial reference picture list 0 may be primarily aligned in thesequence of the short-term reference picture set composed of short-termreference pictures having POCs less than that of the current picture,the short-term reference picture set composed of short-term referencepictures having POCs greater than that of the current picture, and thelong-term reference picture set.

Initial reference picture list 1 may also be primarily aligned in thesequence of the short-term reference picture set composed of short-termreference pictures having POCs greater than that of the current picture,the short-term reference picture set composed of short-term referencepictures having POCs less than that of the current picture, and thelong-term reference picture set.

The decoding device derives position information about the position towhich an inter-layer reference picture set is to be added (S1320). Suchposition information is information signaled by the encoding device tothe decoding device, and may be transmitted, with the positioninformation being included in a slice or sequence level, for example, aslice header or sequence header.

In the case of a bitstream that supports multiple view layers, such asfor multiview scalability, there are many cases where pictures forrespective layers have different characteristics, and have differentcorrelations with a reconstructed picture of a base layer. Further,temporalId values may differ from each other between multiple layers,and the frequencies at which inter-layer reference occurs may differfrom each other depending on the temporalId values.

Depending on such various conditions, the optimal position to which theinter-layer reference pictures are to be added may differ for respectivelayers, and thus the position to which inter-layer reference picturesare to be added may be signaled for respective multiple layers.

When the position information is derived, the decoding device adds theinter-layer reference picture set to the corresponding position of theinitial reference picture list indicated by the derived positioninformation (S1330).

The inter-layer reference picture set may be generated before theposition information is derived, or may be generated simultaneously withthe addition of inter-layer reference pictures to the initial referencepicture list after the position information has been derived.

The initial reference picture list may be composed of pictures havingflag information (used_by_curr_pic_flag) of 1 among reference picturesincluded in the reference picture set, wherein the flag informationindicates whether the corresponding pictures are used as referencepictures.

Here, the sequence of reference picture sets aligned in the initialreference picture list may be set variously according to the positioninformation.

For example, the initial reference picture list 0 may be constructed inthe sequence of a short-term reference picture set composed ofshort-term reference pictures having POCs less than that of the currentpicture, an inter-layer reference picture set, a short-term referencepicture set composed of short-term reference pictures having POCsgreater than that of the current picture, and a long-term referencepicture set composed of long-term reference pictures.

The initial reference picture list 1 may be constructed in the sequenceof a short-term reference picture set composed of short-term referencepictures having POCs greater than that of the current picture, aninter-layer reference picture set, a short-term reference picture setcomposed of short-term reference pictures having POCs less than that ofthe current picture, and a long-term reference picture set composed oflong-term reference pictures.

Alternatively, when the inter-layer reference picture set includesmultiple sub-inter-layer reference picture sets, and the sub-referencelayer picture sets are separated and added to the initial referencepicture list, the position information may include information about theposition to which respective sub-reference layer picture sets are to beadded.

For example, in the case of a layer supporting multiview scalability,initial reference picture list 0 may be constructed in the sequence of ashort-term reference picture set composed of short-term referencepictures having POCs less than that of the current picture, asub-inter-layer reference picture set composed of pictures having a viewsequential position lower than that of the current picture amongmultiview reference layer pictures, a short-term reference picture setcomposed of short-term reference pictures having POCs greater than thatof the current picture, a long-term reference picture set composed oflong-term reference pictures, and a sub-inter-layer reference pictureset composed of pictures having a view sequential position higher thanthat of the current picture among the multiview reference layerpictures.

Initial reference picture list 1 may be constructed in the sequence of ashort-term reference picture set composed of short-term referencepictures having POCs greater than that of the current picture, asub-inter-layer reference picture set composed of pictures having a viewsequential position higher than that of the current picture among themultiview reference layer pictures, a short-term reference picture setcomposed of short-term reference pictures having POCs less than that ofthe current picture, a long-term reference picture set composed oflong-term reference pictures, and a sub-inter-layer reference pictureset composed of pictures having a view sequential position lower thanthat of the current picture among the multiview reference layerpictures.

Alternatively, the inter-layer reference picture set may be generatedbased on the temporal sub-layer index (tempralId) of the currentpicture, or based on the maximum number of temporal sub-layers to whichinter-layer prediction is permitted.

For example, as the temporal sub-layer index (tempralId) of the currentpicture is lower, the inter-layer reference picture set may be alignedat the lower sequential position of the initial reference picture set.In this case, the detailed position to which the inter-layer referencepicture set is to be added may be signaled.

Alternatively, as the difference between the values of the temporalsub-layer index (tempralId) of the current picture and the temporalsub-layer index of the reference layer is smaller, the inter-layerreference picture set may be aligned at the lower sequential position ofthe initial reference picture set. Even in this case, the detailedposition to which the inter-layer reference picture set is to be addedmay be signaled.

Based on a final reference picture list when the final reference picturelist is generated via the modification of the reference picture list orbased on the initial reference picture list when the initial referencepicture list is not modified, the decoding device performs prediction ofthe current picture and decoding of the current picture (S1340).

When the current picture is predicted, reference pictures included inthe inter-layer reference picture set are indicated by long-termreference pictures, and the decoding device uses the reference picturesincluded in the inter-layer reference picture set as reference picturesof the current picture.

Meanwhile, in order to signal the position to which inter-layerreference pictures are to be added, the encoding device must calculatebit rate distortion, in which video quality relative to the number ofbits is considered, for each of the positions to which inter-layerreference pictures can be added, and determine the position to which theinter-layer reference pictures can be added, based on the results ofcalculation. In this case, the encoding computational load that must beperformed by the encoding device may be increased.

In order to reduce the computational load in the encoding stage whilemaintaining variety in pictures for respective multiple layers, theencoding device may limit the number of positions to which referencepictures are to be added to a predetermined number, may set thepositions, to which inter-layer reference pictures can be added, tocorrespond to the predetermined number, and may calculate the bit ratedistortion only for the set positions. Based on the calculated bit ratedistortion, the optimal positions to which the inter-layer referencepictures can be added may be derived, and the encoding device maytransmit information about the positions to the decoding device.

For example, the positions may be set such that the inter-layerreference pictures can be added to three positions, such as the firstposition of the initial reference picture list, the position subsequentto the short-term reference picture set, and the position subsequent tothe long-term reference picture set. In this case, the encoding devicemay encode the indication indices of the positions to which theinter-layer reference pictures are to be added, among the threepositions, and may signal the encoded indices.

The positions to which inter-layer reference pictures are to be addedand indication indices for identifying the positions may be mapped toeach other, as shown in the following Table 1.

TABLE 1 Position to which inter-layer reference Indication picture isadded index First position of initial reference picture list 0Subsequent to short-term reference picture set 1 Subsequent to long-termreference picture set 2

Referring to Table 1, when the inter-layer reference picture is added tothe first position of the reference picture list, an index may be set to0, when the inter-layer reference picture is added to the positionsubsequent to the short-term reference picture set, the index may be setto 1, and when the inter-layer reference picture is added to theposition subsequent to the long-term reference picture set, the indexmay be set to 2.

The position to which an inter-layer reference picture is to be addedmay vary for each layer or each slice. In this case, the indicationindex may be signaled for each layer or each slice.

Further, the indication flag indicating whether the indication index,indicating the position to which the inter-layer reference picture is tobe added, has been transmitted, may be signaled, with the indicationflag being included in the video parameter set of each layer.

FIG. 14 is a diagram showing a method for generating a reference picturelist according to another embodiment of the present invention.

First, the decoding device receives an indication flag that indicateswhether an indication index indicating the position, to which aninter-layer reference picture for each layer is to be added, in theinitial reference picture list has been transmitted, and determineswhether an indication index has been transmitted, based on the receivedindication flag (S1410).

The indication flag may be signaled, with the flag being included in thevideo parameter set of each layer.

When indication flag is 1 (S1420), the decoding device receives andderives the indication index, and derives the position to which aninter-layer reference picture is to be added in the initial referencepicture list for each layer (S1430).

The position to which the inter-layer reference picture is to be addedmay be mapped to the indication index, as shown in Table 1. The decodingdevice may derive the position to which the inter-layer referencepicture is to be added, using the lookup table, as shown in Table 1.

In contrast, when the indication flag is 0 (S1420), the decoding devicemay determine position information about the position to which aninter-layer reference picture set is to be added, from a presetreference picture list (S1440). Thereafter, the decoding device may addthe inter-layer reference picture set to the corresponding position ofthe initial reference picture list, indicated by position informationpreset to a default value, and then constructs the initial referencepicture list (S1450).

The decoding device may perform prediction of the current picture anddecoding of the current picture, based on the initial reference picturelist (S1460).

Steps S1450 and S146 are identical to steps S1330 and S1330, and thus arepeated description thereof will be omitted.

In accordance with the present invention, flag information indicatingwhether the inter-layer reference picture set is separated into at leasttwo sub-reference layer picture sets and then added to the referencepicture list may be signaled. That is, flag information required toeasily recognize the determination of whether an inter-layer referencepicture set is separated into two or more sub-reference layer picturesets may be transmitted from the encoding device to the decoding device.

As described above, when the reference pictures for multiview layers areseparated into multiple sub-reference layer picture sets, the flaginformation is 1.

If the flag information is 1, information about the number ofsub-reference layer picture sets into which inter-layer referencepicture sets are separated may be additionally signaled.

Further, when the flag information is 1, the above-described indicationflag and indication index may also be signaled.

In this way, according to the present invention, there are provided amethod for generating a reference picture list including pictures ofanother layer with respect to a layer to be currently encoded anddecoded, and a device using the method.

The inter-layer reference picture set included in the reference picturelist may be adaptively added to the reference picture list depending onthe characteristics of picture sets, for example, the index of thetemporal sub-layer of the current picture, the difference between theindex values of the temporal sub-layers in layers, or the sequence ofviews.

The method and device for signaling the position information about thepositions, to which inter-layer reference pictures are to be added, inthe reference picture list are included in the scope of the presentinvention. The position information may be individually encoded andsignaled, or may be signaled as index information indicating presetlimited positions.

In the above-described exemplary systems, although methods have beendescribed based on flowcharts as a series of steps or blocks, thepresent invention is not limited to a specific sequence of steps,wherein some steps may be performed in a sequence differing from that ofthe above-described steps, or simultaneously with the steps. Further,since the above-described embodiments include various aspects ofexamples, it should be understood that combinations of the embodimentsalso correspond to embodiments of the present invention. Therefore, itis apparent that the present invention may include all substitutions,modifications and changes belonging to the scope of the accompanyingclaims of the invention.

INDUSTRIAL APPLICABILITY

The present invention may be used to code a video signal having amulti-layer structure.

The invention claimed is:
 1. A method for decoding video supportingmultiple layers, comprising: reconstructing inter-layer referencepictures by decoding corresponding pictures in reference layers forinter-layer prediction of a current picture in a current layer;generating an initial reference picture list based on an inter-layerreference picture set including the inter-layer reference pictures;generating a final reference picture list by modifying the initialreference picture list and performing prediction of a current block inthe current picture based on the final reference picture list and areference picture index of the current block, wherein the initialreference picture list is constructed by using the inter-layer referencepicture set including a plurality of sub-reference layer picture sets,the plurality of sub-reference picture sets including a firstsub-reference layer picture set and a second sub-reference layer pictureset, wherein the initial reference picture list comprises an initialreference picture list 0 and an initial reference picture list 1,wherein the first sub-reference layer picture set is arranged, in theinitial reference picture list 0, between a first short-term referencepicture set including short-term reference pictures having POCs lessthan POC of the current picture and a second short-term referencepicture set including short-term reference pictures having POCs greaterthan POC of the current picture, and the second sub-reference layerpicture set is arranged, in the initial reference picture list 0, at theend of a long-term reference picture set including long-term referencepictures, wherein the first short-term reference picture set, the secondshort-term reference picture set and the long-term reference picture setbelong to the current layer, and wherein the first and the secondsub-reference layer picture sets belong to a different layer from thecurrent layer.
 2. The method of claim 1, wherein the initial referencepicture list 0 is constructed in a sequence of a first short-termreference picture set including short-term reference pictures havingPOCs less than POC of the current picture, the first sub-reference layerpicture set, a second short-term reference picture set includingshort-term reference pictures having POCs greater than POC of thecurrent picture, a long-term reference picture set including long-termreference pictures, and the second sub-reference layer picture set. 3.The method of claim 1, wherein the initial reference picture list 1 isconstructed in a sequence of a second short-term reference picture setincluding short-term reference pictures having POCs greater than POC ofthe current picture, the second sub-reference layer picture set, a firstshort-term reference picture set including short-term reference pictureshaving POCs less than POC of the current picture, a long-term referencepicture set including long-term reference pictures, and the firstsub-reference layer picture set.